The present invention relates to a signal formation apparatus for use in an interference measurement, more particularly to a signal formation apparatus used for in interference measurement apparatus for measuring a displacement of a scale section.
A structure of a conventional interference measurement apparatus is illustrated in FIG. 17.
The conventional interference measurement apparatus (encoder) comprises a laser diode 101; a collimator lens 102; a deflection beam splitter 103; reflection members 104a and 104b; diffraction gratings 105a and 105b; a scale 106; a 1/4 wave plate 107; a beam splitter 108; polarizing plates 109a and 109b; detectors 110a and 110b; and a reflection mirror 111.
A coherent light emitted from the laser diode 101 undergoes a collimation by the collimator lens 102, that is, the coherent light is converted to a parallel beam. This parallel beam is divided into a P polarized light in a transmission direction and a S deflected light in a reflection direction by the deflection beam splitter 103. The deflected light beams are irradiated perpendicularly onto the diffraction gratings 105a and 105b by the reflection members 104a and 104b. Diffracted lights LD1 and LD2 are irradiated onto a measurement diffraction grating 106A on the scale 6 from two directions. The lights LD1 and LD2 are diffracted and reflected by the diffraction grating 106A in the direction perpendicular to the diffraction grating 106A on the scale 16. The light LD1 and LD2 become .+-.m ordered re-diffracted lights LD1(m) and LD2(-m), respectively, thus travelling on the same optical path toward a detection optical portion. The re-diffracted lights are perpendicularly polarized with each other and passes through the 1/4 wave plate 107 via the reflection mirror 111, and become circularly polarized lights, respectively. The circularly polarized lights are divided so as to travel along two optical paths by the beam splitter 108, and respectively subjected to a photoelectric detection by the detectors 110a and 110b after passing through the polarization plates 109a and 109b.
Next, a structure of a conventional optical waveguide laser Doppler velocimeter device will be shown in FIGS. 18A and 18B.
As shown in FIG. 18A, in a optical substrate 200, provided are an optical waveguide 201 for receiving an inputted light; a dividing section 202; a frequency shifter 203; an optical waveguide 204 for outputting an outputted light; and a block 205. Moreover, in the optical substrate 200, an optical waveguide device 206 and a micro Fresnel lens 207 are respectively provided in combination with each other. An array composed of three micro Fresnel lenses is fixed to the end face of the block 205. In FIG. 18B, the structure of the micro Fresnel lens array is illustrated.